In general, a system including a tape device which records data in a physical medium such as a magnetic tape and an RAID (redundant arrays of inexpensive disks) device which virtually stores the data recorded in the tape device has been widely used as a virtual tape system.
A general virtual tape system will be described with reference to FIG. 5, for example. FIG. 5 is a diagram illustrating a configuration of a general virtual tape system. As illustrated in FIG. 5, a virtual tape system 900 includes a virtual tape device 910 and a tape library device 920. The virtual tape system 900 is communicably connected to a host 930.
The virtual tape device 910 includes a TVC (tape volume cache) 911 which stores data of a plurality of logical volumes (LVs). The TVC 911 uses a RAID device, for example, as a cache. The tape library device 920 includes drives 921 to which magnetic tapes 922 are loaded, respectively.
In the virtual tape system 900 configured as described above, a logical volume written from the host 930 is temporarily stored in the TVC 911. Thereafter, the logical volume is written in a physical volume (PV) included in the tape library device 920 when being output to the tape library device 920. This operation is referred to as “migration”.
Upon receiving a request for mounting a logical volume from the host 930, the virtual tape device 910 determines whether the logical volume is included in the TVC 911. When it is determined that the TVC 911 does not include the logical volume and the mount request represents a reading request, the virtual tape device 910 reads the logical volume, which is a target of the mount request, from the tape library device 920 to the TVC 911. An operation of reading data of a logical volume included in a magnetic tape of the tape library device 920 to the TVC 911 as described above is referred to as “recall”.
Japanese Laid-open Patent Publication No. 2011-123834 and Japanese Laid-open Patent Publication No. 2002-170295 disclose related techniques.
In the general virtual tape system, however, there arises a problem in that data of a logical volume may not be swiftly read at a time of recall.
A virtual tape device unconditionally reads data of a logical volume from a magnetic tape mounted in a tape library device at the time of recall and a long period of time is used for an operation of mounting the magnetic tape on a drive and an operation for positioning in the drive. Thus, if the magnetic tape has not been mounted on the drive, a long period of time is used for the operation of mounting the magnetic tape or the like. Accordingly, the data of the logical volume is not swiftly read.
Note that the problem described above occurs not only in the case of a magnetic tape but also a case of a general tape such as a paper tape.